The Modern Analog Technique is a calibration method for reconstructing a past environmental parameter (e.g. temperature) from faunal assosications. It works by finding modern sites with faunal associations close to those in downcore samples. Environmental data from the modern sites are then used to estimate the environment downcore.
The (single) environmental variable, usually temperature, enters in the first column, and taxa in consecutive columns. All the modern sites, with known values for the environmental variable, go in the first rows, followed by all the downcore samples (these should have question marks in the environmental column).
The plot on the first tab shows all the modern samples, with the observed temperature (for example) versus the MAT reconstructed temperature using cross-validation.
Parameters to set
- Weighting: When several modern analogs are linked to one downcore sample, their environmental values can be weighted equally, inversely proportional to faunal distance, or inversely proportional to ranked faunal distance.
- Distance measure: Several distance measures commonly used in MAT are available. "Squared chord" has become the standard choice in the literature.
- Distance threshold: Only modern analogs closer than this threshold are used. A default value is given, which is the tenth percentile of distances between all sample pairs in the modern data. The "Dissimilarity distribution" histogram may be useful when selecting this threshold.
- N analogs: This is the maximum number of modern analogs used for each downcore sample.
- Jump method (on/off): For each downcore sample, modern samples are sorted by ascending distance. When the distance increases by more than the selected percentage, the subsequent modern analogs are discarded.
Note that one or more of these options can be disabled by entering a large value. For example, a very large distance threshold will never apply, so the number of analogs is decided only by the "N analogs" value and optionally the jump method.
Cross validation
The scatter plot and R2 value show the results of cross-validation within the modern data. It may be noted that for MAT, leave-one-out (jackknifing) is not necessary because there is no global model based on all samples. The y=x line is shown in red. This only partly reflects the "quality" of the method, as it gives little information about the accuracy of downcore estimation.
Dissimilarity distribution
A histogram of all distances in the core-top (modern) data.
Semivariogram
Shows a semivariogram of variance in the environmental variable as a function of faunal difference. Several semivariogram models can be fitted. This type of plot is familiar from spatial geostatistics, but is also useful for MAT because it gives a good impression of the degree of “noise” in the faunal data with respect to environmental prediction.
Reconstructions
Reconstruction of the paleoenvironmental values using MAT.